Changing lift pump in 98 12V (long)

[CJ Johansson]

Well, a few days ago I posted about the lift pump dying in my 98 12V. This ended up taking out the diesel fuel heater (smoked it) due to lack of fuel cooling. Luckily, if you take the center bolt out from above the strainer screen, the heater element comes out and you can put the strainer bowl back on without the heater. I still need to see if I can get just the heater and cable, but that's another thread...

As for the pump, I couldn't really test the check valves, but there was a fairly big groove worn in the piston bore, probably from a grain of sand or something that made it past the strainer. I feel like it might be a good idea to put a finer filter between the strainer and pump, but I'm not sure what to use yet.

Anyway, the ******* wouldn't tell me whether the lift (transfer) pump was covered under the 100K warranty, so I eventually decided to change the pump myself after getting some excellent advice on the Truck 911 forum from Joe Donnely and others. I figured that since other folks may eventually need to do this, I'd write up a fairly detailed description of just what it takes to do this job. Sorry, no pictures. Changing the pump outdoors in a snow storm with barely enough light (I don't have a shop/garage, or power, or even a house right now, just a 5th wheel trailer) made pictures basically impossible.

So, on with the pump change. As Joe said, it can be done from the top, and in my case, lying in the snow under the truck didn't sound like much fun, so from the top it was. It was fairly easy, took about 4 hours, but would be much faster the next time now that I've done it once. Once you get the steel air boost tube from the intercooler to the intake horn out of the way and remove the fuel filter, you have quite a bit of room to work.

Tools needed:
7/16 or 11mm socket - for boost tube clamps
10mm socket - for lift pump bolts
14mm socket - for fuel filter canister
3/8 ratchet
6" 3/8 extension
3/8 universal joint - makes filter nut easier
3/4" open end wrench - for fuel inlet nut
14mm open end wrench - for fuel outlet fitting
19mm open end wrench - injector line nuts

May need:
17mm socket - fuel strainer bowl
5/16 hex wrench (allen) - to remove heater element
12mm socket - upper banjo on fuel filter inlet
17mm open end - lower banjo on fuel filter inlet

Parts:
Transfer (lift) pump: Cummins 3936316 (new number)
gaskets (2 req'd): Cummins 3931059 (new number)

Cummins wanted $165 for the pump, the local Kenworth dealer wanted $149.83. The gaskets were $1.28 each.

First, use the 7/16 or 11mm to remove the boost tube. Remove the band at the intercooler outlet and the band at the intake horn. Take the tube out along with the rubber connection boots.

Remove the fuel filter canister. Open the bleed screw with 10mm wrench, drain fuel with the water drain valve, unhook water in fuel sensor connector, remove canister with 14mm socket, U-joint, and extension. With the bost tube removed, getting the canister out is really easy.

Now you have access to the pump and almost a good view of the thing. Removing the pump also removes the strainer/heater assembly. Disconnect the cable going to the heater at the plug about 6 inches up the cable from the heater. Remove the fuel inlet fitting from the top of the strainer with a 3/4 open end wrench. Next, the fuel outlet tube from the pump to the fuel filter needs to be removed. Apparently, on some engines, this can be done by removing the banjo fittings on the top of the filter housing (12mm for top bolt, 17mm for lower). This will allow you to use the steel line as a handle to remove the filter. On mine, this was not possible since the outlet line ran behind the steel inlet line. I removed the fuel outlet fitting from the pump with a 14mm open end wrench.

Next, use a 10mm socket, 6" extension and 3/8 ratchet handle. There are 2 bolts, one behind the pump, the other between the pump and the strainer/heater. There's not a whole lot of room between the strainer and pump, but unless you have really huge sockets, there's plenty of room. These 2 bolts hold both the fuel strainer/heater and the pump in place. This is why you need 2 gaskets, one between the block and the strainer bracket, the other between the bracket and the pump.

The pump is now free to be removed, take it out the same way you got the fuel filter out by threading it between the block and the wiring harness the same way you got the fuel filter canister out.

The pump is attached to the strainer by a length of rubber hose and spring type clamps. Use a vise grip type plier to squeeze the tabs on the clamp at the pump and slide up the hose a few inches. Pull the hose from the pump. Remove the elbow fitting that the hose was on from the old pump, since the new one doesn't come with this. You're now ready to put the new pump on.

Clean all the old gaskets & pieces from the strainer bracket and block. Install the elbow fitting to the new pump, use some pipe fitting sealer such as Harvey's PTFE paste. Use a small amount on the male threads of the elbow fitting. This will keep the amount of goop that gets inside to a minimum. If the plunger rod on the old pump in in good shape, it is suggested to use it with the new pump since it's worn into the cam in the engine. The rod just pulls strainght out of the pump. Use some cam lube (Crane's, lubriplate, etc.) on both ends of the plunger rod and oil the rod before installing.

Place one gasket on the pump and thread the plunger through the strainer bracket. Reattach the fuel hose to the elbow and replace the clamp. Put the other gasket on the back side of the strainer bracket and put the bolts through the 2 holes. The gaskets have little tabs in their holes that kind of hold the bolts and gaskets in place, but a bit of gasket sealer helps too.

Thread the pump back down into place. Getting the bolts started is kind of difficult. Attaching the steel fuel inlet and outlet lines helps hold it in position while you fumble with getting the bolts started. Once the bolts are tight, attach the fuel heater plug. Reinstall the fuel filter and attach the water in fuel sensor plug. Reinstall the air boost tube at the intercooler, then at the intake horn.

Now you're ready to prime the fuel system. Open the bleed screw and pump the primer button until fuel comes out the bleed screw. Tighten the bleed screw and pump the plunger a few more times until you hear fuel squirting through the overflow valve on the injector pump.

Since the lift pump probably died and you ran out of fuel, you probably need to bleed the injector lines. Loosen the fittings at the top of the injectors with a 19mm wrench. They don't need to be removed, just loosen a bit. Crank the engine until fuel comes out of the fittings on the injectors. This could take bit of cranking, so it'd be a good idea to have a set of jumper cables and another vehicle available, especially if it's cold and/or your batteries aren't in tip top shape. Follow the general precautions on excessive cranking to avoid overheating your starter - don't crank for more than 30 sec., let things cool for a few minutes before cranking again.

Once fuel is to the fittings, tighten the fittings on the injectors. Go back to cranking again. The engine will likely sputter to life and promptly die a few times before it takes off and runs. It may run rough for a few seconds, but will eventually smooth out.

-cj